Full verification of the liquid exclusion-adsorption chromatography theory using monolithic capillary columns

Capillary electrochromatography (CEC) was used to separate alkyl phenol ethoxylates (APEs) as model diblock copolymers, with monolithic polymers as stationary phases. The order of elution indicate that the two polymer blocks follow distinct chromatographic modes: size-exclusion for the poly(oxyethylene) group and adsorption interaction for the alkyl part. Therefore, our experimental results were compared to the theory describing liquid exclusion-adsorption chromatography (LEAC). They were found in perfect agreement with the theory, which turned to be verified for the first time over the full range of polymer lengths.     

Single potential electrophoresis microchip with reduced bias using pressure pulse injection

We propose two variants of a new injection technique for use in electrophoresis microchips, called "front gate pressure injection" and "back gate pressure injection", that both enable a controlled and reproducible sample introduction with reduced bias compared to electrokinetic gated injection. A continuous flow of a test solution of fluorescein/rhodamine B in 20 mM Tris/boric acid buffer (pH 8.6) sample test solution is electrokinetically driven near to the entrance of the separation channel, using a single voltage (3 kV) that is constant in time. A sample plug is injected in the separation channel by a pressure pulse of the order of 0.1 s. The latter is generated using the mechanical deflection of a PDMS membrane that is loosely placed on a dedicated chip reservoir. The analysis of the peak area ratio of the separated compounds demonstrates a nearly constant sample composition when using pressure-based injection. A small remaining injection bias for the shortest membrane deflection times can be attributed to a dilution effect of the charged compound due to the presence of an electrical field transverse to the sample flow boundary in the channel junction.     

Ionic jump processes and high field conduction in glasses

A theory of multiple-ion jumps is proposed to explain the large apparent jump distances which have been calculated from high field conduction in glasses. An analysis of published data on correlation coefficients suggests that multiple ion jumps up to about four ions at a time may occur in single-alkali glasses. In mixed-alkali glasses such processes are shown to be less probable. Measurements of high field conductivity were made on both single- and mixed-alkali glasses, using blown membranes between N/10 acid solutions. The onset of departures from Ohm's law occurred at fields of about 10⁷ V m^?1 from which a jump distance of about 25–30 Å is calculated. This is too large for the proposed multiple-ion jump processes suggested, and, furthermore, the high field currents followed the Poole-Frenkel (PF) law. An alternative theory is given in which the PF law is derived for ionic migration: shallow coulombic potential basins are assumed to be distributed throughout the volume of the glass, owing to non-bridging oxygens whose charge is not balanced by cations on adjacent sites.     

Effect of an angular bias on LDA measurements in supersonic turbulent flow

The problem of a laser Doppler anemometer's statistical response to the velocity direction of particles scattering in space has been studied for many years. This phenomenon introduces a statistical bias distinct from the classical bias related to velocity fluctuations. Though the latter has corrected some controversial application, the only answer found to counter the angular bias remains, for most experimenters, the utilization of Bragg cells. It is not always possible to use such a device, however, and this is particularly true in supersonic flows. The angular bias, inevitable in this case, shows increased effects when the normal to the fringe plane is inclined with respect to the mean velocity direction. Analysis of the phenomenon in the more complex case of a two-component anemometer and a supersonic flow helps to show how measurements of velocity fluctuations in a boundary layer quite close to the wall may include significant errors because of this bias.     

Study of structural and electronic transport properties of Ce-doped LaMnO3

The structural and electronic transport properties of La_1−x Ce _x MnO₃ (x=0.0–1.0) have been studied. All the samples exhibit orthorhombic crystal symmetry and the unit cell volume decreases with Ce doping. They also make a metal-insulator transition (MIT) and transition temperature increases with increase in Ce concentration up to 50% doping. The system La_0.5Ce_0.5MnO₃ also exhibits MIT instead of charge-ordered state as observed in the hole doped systems of the same composition.